Nervous System and Endocrine Glands: Hormones and Functions

The correct answer is B, the brain. The brain is the organ that interprets pain, but its own tissue has no pain receptors, so cutting or pricking it causes no sensation; the covering membranes, the blood vessels and the scalp do have receptors, which is why a headache hurts. This is the reason brain surgery can be performed on a patient who is awake and talking, with only the scalp anaesthetised. Option A is wrong because the skin is the richest field of pain receptors in the body and a needle prick there is the standard example of a painful stimulus. Option C is wrong because the heart has pain receptors and signals its distress as the crushing pain of angina, often felt in the left arm as referred pain. Option D is wrong because the cornea of the eye is among the most sensitive tissues of the body, which is why the smallest speck of dust in it is unbearable.

The correct answer is B, the thyroid gland, a butterfly-shaped gland in front of the windpipe in the neck, which is the largest purely endocrine gland in the body and secretes thyroxine, triiodothyronine and calcitonin. Option A is wrong because the pituitary is the smallest endocrine gland, about the size of a pea, although it is the master gland that controls several others, so the two make a standard pair of opposites in exams. Option C is wrong because the adrenal glands, one above each kidney, are small, and they are remembered for adrenaline rather than for size. Option D is wrong on a technicality worth knowing: the pancreas is larger than the thyroid, but it is a mixed or heterocrine gland, part exocrine for digestive juice and part endocrine for insulin, so the largest purely endocrine gland remains the thyroid.

The correct answer is B, the cerebellum, which lies below and behind the cerebrum and coordinates the work of the muscles so that movement is smooth and the body stays balanced; this is why a person whose cerebellum is affected by alcohol staggers. Option A is wrong because the cerebrum, the largest part of the brain, is the seat of thought, memory, intelligence and the will to move, but not of the fine coordination that follows the order. Option C is wrong because the medulla oblongata governs the involuntary actions that keep a body alive, the heartbeat, breathing, blood pressure, vomiting, sneezing and coughing. Option D is wrong because the thalamus is a relay station that sorts sensory impulses and passes them on to the cerebrum. Keep the trio apart: cerebrum for thinking, cerebellum for balance and medulla for the involuntary.

The correct answer is B, the pituitary, a pea-sized gland lodged in a bony socket at the base of the skull and attached to the hypothalamus. It is called the master gland because its secretions control other glands: thyroid stimulating hormone drives the thyroid, adrenocorticotropic hormone the adrenal cortex, and the gonadotropins the testes and ovaries, besides its own growth hormone. Option A is wrong because the thyroid is itself under the pituitary's command, and its claim to fame is being the largest endocrine gland. Option C is wrong because the pineal gland secretes melatonin and keeps the daily rhythm of sleep, a narrower task. Option D is wrong because the thymus secretes thymosin for the training of the immune cells and shrinks after puberty, so it neither controls other glands nor lasts a lifetime.

The correct answer is B, the beta cells of the islets of Langerhans in the pancreas. Insulin lowers the level of glucose in the blood by helping the cells take it in and by having the liver store it as glycogen, and a want of insulin or a failure of the body to respond to it causes diabetes mellitus. Option A is wrong because the alpha cells of the same islets make glucagon, which does the opposite and raises blood sugar; the two hormones together keep the level steady, and swapping them is the commonest error in this question. Option C is wrong because the adrenal medulla secretes adrenaline and noradrenaline; adrenaline also raises blood sugar, but it is not insulin. Option D is wrong because the thyroid follicles make thyroxine, which sets the rate of metabolism and contains iodine.

The correct answer is A, goitre. Iodine is needed to make thyroxine, so when the diet is short of it the thyroid gland works harder and enlarges into a visible swelling of the neck called goitre; a severe shortage in a growing child causes cretinism and in an adult myxoedema, and iodised salt is the standard preventive. Option B is wrong because rickets, which softens and bends the bones of children, is caused by a deficiency of vitamin D and of calcium, not iodine. Option C is wrong because scurvy, with bleeding gums and slow healing, comes of a want of vitamin C, the sailor's disease cured by citrus fruit. Option D is wrong because beri-beri, with weakness of the nerves and muscles, follows a deficiency of vitamin B1 or thiamine, common where polished rice is the staple. Only goitre belongs to a mineral of the thyroid.

The correct answer is B, 12 pairs. The cranial nerves arise from the brain and serve the head and neck, among them the optic nerve of sight, the auditory nerve of hearing, the olfactory nerve of smell and the vagus, which is the longest cranial nerve and reaches down to the heart, lungs and stomach. Option A is wrong because ten is the number in some lower vertebrates such as fishes and amphibians, which is why it is offered as a distractor. Option C is wrong because 31 pairs is the number of spinal nerves, which arise from the spinal cord, and the two figures must be kept apart: 12 cranial and 31 spinal. Option D is wrong because 33 is the number of vertebrae in the human vertebral column at birth, a different count altogether, fused later into 26 bones in an adult.

The correct answer is C, adrenaline, also called epinephrine, secreted by the medulla of the adrenal gland in fright, anger or stress. It quickens the heartbeat, raises the blood pressure, widens the air passages, sends more blood to the muscles and releases glucose from the liver, so that the body is ready to fight or to run. Option A is wrong because insulin lowers blood sugar and works in the quiet business of storing energy, the opposite of an emergency. Option B is wrong because thyroxine sets the long-term rate of metabolism and works over days and weeks, not seconds. Option D is wrong because oxytocin, from the posterior pituitary, causes the contraction of the uterus at childbirth and the ejection of milk, and is often called the birth hormone. The adrenal cortex, by contrast, makes cortisol for longer-term stress.

The correct answer is C, the medulla oblongata, the lowest part of the brain stem, which joins the brain to the spinal cord and holds the centres for the heartbeat, for breathing and for the width of the blood vessels, as well as for vomiting, sneezing, coughing and swallowing. An injury here is fatal because these actions cannot be done at will. Option A is wrong because the cerebrum directs voluntary action and thought. Option B is wrong because the hypothalamus regulates body temperature, hunger, thirst and sleep and controls the pituitary, which is a related but different list, and a question may well test the difference. Option D is wrong because the cerebellum looks after balance and the coordination of movement. The three to fix are cerebrum for the voluntary, medulla for the involuntary and hypothalamus for the internal environment.

The correct answer is C, the sciatic nerve, which is also the thickest nerve in the body. It is formed from the roots of the lower spine, passes through the buttock and runs down the back of the thigh to the leg and foot, and its compression by a slipped disc causes the pain called sciatica. Option A is wrong because the vagus, the tenth cranial nerve, is the longest of the cranial nerves and travels from the brain to the heart, lungs and gut, but it is shorter than the sciatic; the two records are often confused, so remember sciatic for the body and vagus for the cranial nerves. Option B is wrong because the optic nerve is short, carrying impulses from the retina to the brain. Option D is wrong because the trigeminal, the largest cranial nerve by thickness, serves the face and the muscles of chewing.